Nonequilibrium fluctuations in the current and electron temperature in a semiconductor

Nonequilibrium low-frequency fluctuations in the current and electron temperature. The nonequilibrium nature of the fluctuations results from the imposition of an external electricfield. Explicit expressions are found for the spectral functions for the current and electron temperature for various energy- and momentum-dissipation mechanisms. The nature of these functions differs from that in the equilibrium case, in that there is an additional dispersion, whose frequency dependence may be nonmonotonic. In a piezoelectric semiconductor, in the case of momentum dissipation at ionized impurities, there exists acritical field at which the spectral functions for the fluctuations in the current and electron temperature become infinite, due tothe appearance of a superheating instability.